Beginning in 1993, all highway diesel fuel in the United States was required to have a minimum sulfur content of 0.05% (by weight). Refineries have been able to meet this standard by hydrotreating. Hydrotreating removes sulfur, nitrogen and other metal-bonding reactive sites as well as seal-swelling and lubricating aromatic compounds. However, a major drawback to the hydrotreating process used to reduce sulfur and aromatic levels is that the diesel fuel product has reduced fuel lubricity. The reduced fuel lubricity increases wear rates in many fuel injection systems, as such injections systems have been designed to utilize natural lubricating properties of traditional diesel fuels (typically containing 0.2 to 0.5% by weight sulfur or 2000-5000 ppm). This has caused a dramatic increase in fuel injection system problems manifest as under run and stalling as the most minor to injector nozzle fouling, to fuel pump failures resulting in a need to replace entire systems. This is causing fuel injection systems to be redesigned even as injection pressures have risen to the detriment of wear and mechanical performance.
Distillate petroleum hydrocarbon fractions in the kerosene/diesel fuel range have essentially no lubricity or lubricating value. The high solvent action of the fuel and the constant washing by large volumes of fuel make it impossible to maintain lubricant on pump surfaces. Thus, fuel pumps are subjected to serious wear, leading to pump failure. Fuel compositions have to be treated (formulated) to address wear, erosion and corrosion problems.
Petroleum refineries produce 50 to 60 billion gallons of diesel fuel for consumption in the United States each year. Most refineries are producing only low-sulfur diesel fuels to achieve economies of scale. This means that, even though off-road vehicles are currently exempt from the low-sulfur emission requirements, most, including tractor and other farm equipment, will be using low-sulfur diesel fuels. This will result in increased engine wear in agricultural equipment that was designed for the natural lubricating properties of diesel fuels. The EPA is in the process of developing emission standards for off-road engines which will also cause low-sulfur diesel fuels to be used.
Traditional fuel lubricity additives contain sulfur, phosphorous, zinc, nitrogen or boron. These are called ash forming or catalyst-poisoning additives. Ash forming additives are thermally activated and form sacrificial chemical bonds to metal surfaces. The additive will then "shear" from the metal surface before the metal itself, resulting in protection of the metal surface from wear. Many additives also contribute to particulate emissions during combustion. Moreover, additives can form SO.sub.x, NO.sub.x and PO.sub.x emissions, or emissions which can poison a catalyst used in catalytic converters, causing an increase in particulate and hydrocarbon emissions.
Therefore there is a need in the art for diesel fuel additives that impart needed lubricity properties but provide minimal ash or preferably ash-less properties for the purposes of reducing ultimate emissions characteristics. The present invention applies telomer technology to this field of art to provide an improved ashless additive to diesel fuel and kerosene that provides lubricity properties, improved combustion and improved emissions characteristics. The goal, that was achieved by this invention, was to provide a fully fuel-soluble additive molecule, which is derived from renewable sources and contains no ash or deposit-producing elements or catalyst poisons such as sulfur, phosphorous or boron. The invention describes the achievement of that goal.